Inserting an extra gene, researchers produced a strain of mice that excelled in a range of tasks, like recognizing a Lego piece they'd encountered before, learning the location of a hidden underwater platform and recognizing cues that they were about to receive a mild shock.
The findings, published in the Thursday issue of Nature, indicate a common mechanism lies at the root of all learning, identify the protein NR2B as a key to brain function. The research could lead to a drug to treat memory disorders, such as Alzheimer's, by increasing NR2B levels, Tsien said.
The mice carried the enhanced abilities into adulthood, when learning ability and memory naturally taper off, and passed their heightened learning abilities on to their offspring.
"This points to the possibility that enhancement of learning and memory or even IQ is feasible through genetic means, through genetic engineering," said Joe Z. Tsien, the assistant professor of molecular biology at Princeton University who led the research team.
Production of NR2B protein normally decreases with age, correlating with the loss of memory and learning ability commonly experienced by older people, Tsien said.
The new mouse work represents a breakthrough in understanding how the brain functions at the molecular level, said Dr. Robert Malenka, a psychiatrist and behavioral sciences specialist at Stanford University School of Medicine.
"To jump from this very elegant molecular work in a mouse model to humans is a very, very big jump," said Malenka. "Nevertheless, it is a jump we can make and will make eventually. When we jump to humans, it will probably be a lot more complicated."
One complication is the risk that any drug that would increase NR2B levels could also increase the risk of stroke, because both stroke and learning are related to the same neurological switches in the brain, Malenka added.
Dr. Ron McKay of the National Institute of Neurological Disorders and Stroke said drug companies are already investigating manipulation of NR2B levels to treat strokes. Any research that illuminates how NR2B works in the brain would be valuable in that work, he said.
The prospect of genetically engineering smarter babies raises big ethical questions.
Because of the inherent risks, it makes more sense ethically to begin applying this discovery to treating diseases and disorders, rather than trying to create smarter babies, Caplan added.
"I wouldn't say I would be worried quite yet about seeing hordes of tiny Einsteins in my neighborhood," he said.
But just as parents strive to improve their children by sending them to better schools or giving them piano lessons, there will be those who want to genetically enhance their offsring, said Caplan. As in other areas of life, the rich would have an advantage.
"We already have a brain gap in this society when some children go to kindergartens that cost $15,000 a year and other children go to kindergartens that don't have adequate plumbing," he said.
Tsien nicknamed the smart mice "Doogie" after the teen-age genius in the television show Doogie Howser, M.D.
Using a tiny glass needle, the scientists injected a gene carrying a blueprint for the protein NR2B into the nucleus of a fertilized mouse egg, then implanted the resulting embryo into the uterus of a mother mouse.
Mice born with the extra gene made more NR2B than usual in their brains.
That extra production boosted mental abilities by enhancing the function of brain-cell switches called NMDA receptors. The results confirm the idea, proposed in 1949, that these switches play a key role in learning.